1. Field of the Invention
The present invention relates to a separation and recovery process of lysine by concentrating a lysine-containing elution liquid with a reverse osmosis membrane, which elution liquid has been eluted from a lysine-adsorbing cation exchange resin with ammonia water. The present invention relates also to a lysine production process in which ammonia permeated through a reverse osmosis membrane with water is recovered and recycled as a resin elution agent or a regeneration agent for the next cycle of the resin treatment.
2. Description of the Related Art
Lysine is one of the most important amino acids as a cattle feed additive and is produced mainly by the fermentation method.
As to the treatment process of a lysine fermentation liquid, the method with the use of a strongly acidic cation exchange resin has been generally applied. This method, for example, is to elute lysine with the use of a low-priced elution agent such as ammonia water, after adsorbing lysine by contacting a lysine fermentation liquid conditioned to a certain pH, with a salt-type cation exchange resin such as ammonium-type one.
As a method to recover lysine from a resin elution liquid, a known method is to crystallize and separate a lysine mineral acid salt (lysine hydrochloric acid salt, lysine sulfuric acid salt, for example) by neutralization with addition of an acid, after concentration under a reduced pressure at an elevated temperature. In this method, it was possible to recycle, the dilute ammonia water obtained through condensation of ammonia-containing vapor as a part of elution agent of the cation exchange resin. In this method, however, there was a weak point that a great amount of heat energy is needed, such as latent heat necessary for evaporation, other than sensible heat. Furthermore, it was inevitable that lysine reacted with other impurities by the heat, which resulted in quality deterioration and yield reduction, such as browning of a liquid and decomposition of lysine.
On the other hand, from the viewpoint of environmental preservation, ammonia vapor produced is harmful and recovery by a cooling system is not perfect. To prevent its discharge into the air, measures are taken, for example, by absorbing with acid liquid or catching with current water. A great amount of cost had been needed to observe the nitrogen content regulation and pH regulation specified for discharged water.